Wayland support

Based on the original port to Wayland by: Joel Teichroeb, Benjamin Franzke, Scott Moreau, et al.

Additional changes in this commit, done by me:

* Wayland uses the common EGL framework
* EGL can now create a desktop OpenGL context
* testgl2 loads GL functions dynamically, no need to link to libGL anymore
* Assorted fixes to the Wayland backend

Tested on the Weston Compositor (v1.0.5) that ships with Ubuntu 13.10,
running Weston under X. Tests ran: testrendercopyex (all backends), testgl2, testgles2,testintersections

include/SDL_syswm.h

@@ -101,6 +101,7 @@ typedef enum
     SDL_SYSWM_UNKNOWN,
     SDL_SYSWM_WINDOWS,
     SDL_SYSWM_X11,
+    SDL_SYSWM_WAYLAND,
     SDL_SYSWM_DIRECTFB,
     SDL_SYSWM_COCOA,
     SDL_SYSWM_UIKIT,
@@ -175,6 +176,14 @@ struct SDL_SysWMinfo
             Window window;              /**< The X11 window */
         } x11;
 #endif
+#if defined(SDL_VIDEO_DRIVER_WAYLAND)
+        struct
+        {
+            struct wl_display *display;            /**< Wayland display */
+            struct wl_surface *surface;            /**< Wayland surface */
+            struct wl_shell_surface *shell_surface; /**< Wayland shell_surface (window manager handle) */
+        } wl;
+#endif
 #if defined(SDL_VIDEO_DRIVER_DIRECTFB)
         struct
         {